¹⁸F-FDG PET patterns and BAL cell profiles in pulmonary sarcoidosis

Purpose Bronchoalveolar lavage (BAL) and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) PET can both demonstrate sarcoid activity. To assess whether metabolic activity imaged by ¹⁸F-FDG PET represents signs of disease activity as reflected by BAL, ¹⁸F-FDG PET patterns were compared with BAL cell profiles. Methods In this retrospective analysis, 77 newly diagnosed pulmonary sarcoidosis patients underwent BAL and ¹⁸F-FDG PET. Based on ¹⁸F-FDG PET, patients were diagnosed with exclusively mediastinal/hilar activity (group A) and activity in the lung parenchyma (group B). Per group, BAL lymphocytes (%), CD4/CD8 ratio, CD103 ⁺CD4⁺/CD4⁺ ratio and neutrophils (%) were compared with the extent of metabolic activity expressed as the maximum standardized uptake value (SUV_max). Additionally, SUV_max and BAL parameters per radiographic stage were analysed. Results Overall, the SUV_max in the lung parenchyma correlated with neutrophils and SUV_max of the mediastinum/hila correlated with the CD4/CD8 ratio. In both groups, a significant, negative correlation between the SUV_max of the mediastinum/hila and the CD103⁺CD4⁺/CD4⁺ ratio was found. In group B, the SUV_max of the mediastinum/hila correlated with the CD4/CD8 ratio, while the SUV_max in the lung parenchyma correlated with the CD103⁺CD4⁺/CD4⁺ ratio and neutrophils. Significant differences were found in the SUV _max, CD4/CD8 ratio, CD103⁺CD4⁺/CD4⁺ ratio and neutrophils between the radiographic stages. The SUV_max of the lung parenchyma was positively related to the radiographic stage, while the SUV_max of the mediastinum/hila and CD4/CD8 ratio were inversely related. Conclusion ¹⁸F-FDG PET correlates with the CD4/CD8 ratio and neutrophils, suggesting that ¹⁸F-FDG PET represents this specific cell profile in BAL. High SUV_max values of the lung parenchyma may therefore correlate with more severe parenchymal involvement, particularly when accompanied by a low SUV_max of the mediastinum/hila.